1. Field of the Invention
This invention relates to a polycrystal piezoelectric device consisting of crystals which have a piezoelectric phase and are oriented in different specific directions.
2. Prior Art Statement
Piezoelectric devices which convert electrical energy to mechanical oscillation are well known and are formed of ferroelectric materials such as barium titanate, PZT and the like or of nonferroelectric materials such as Ba.sub.2 TiBe.sub.2 O.sub.2, Li.sub.2 B.sub.2 O.sub.7 and the like.
Piezoelectric devices made of ferroelectric material are generally fabricated by subjecting a sintered ferroelectric material body to polarizing treatment for obtaining a device whose crystals are polarized in the same direction.
On the other hand, in the case where barium titanate crystals or other such crystals having a piezoelectric phase are obtained by crystallization from glass, the crystals uniformly precipitated by nucleation treatment are also subjected to polarizing treatment for orientation in the same direction. Since, similarly to the case of fabricating a piezoelectric device of ferroelectric material, the polarizing treatment cannot be conducted so as to polarize the different crystals having a piezoelectric phase in different directions, the resulting piezoelectric device exhibits uniform crystallographic orientation.
In a piezoelectric device wherein the crystals having a piezoelectric phase are oriented uniformly in the aforesaid manner, oscillation is produced in a specific frequency mode throughout the entire device. In contrast, in a device in which the orientation of the crystals with piezoelectric phase varies, strictly speaking the oscillation mode differs at different portions of the device and the various individual oscillations interact to form a complex composite oscillation. The device thus resembles one obtained by bonding together a number of different piezoelectric devices and, compared with a device having uniform crystallographic orientation, possesses a functional gradient differing in symmetry.
One object of this invention is thus to provide a polycrystal piezoelectric device of a novel structure in which the oscillation mode differs between different positions thereof.
Another object of the invention is to provide a method of producing such a device.